Abstract

Anterior cruciate ligament (ACL) injury is a major cause of significant time loss to sports participation, as well as reportedly leading to an increased risk of osteoarthritis (OA). Knee instability and functional adaptations are likely to occur following injury to the ACL, despite many ACL-deficient (ACLD) patients displaying no, or minimal, visible impairment. ACL reconstruction (ACLR) is the most common form of treatment for physically active individuals following an ACL injury. The aim of most individuals is to return to preinjury levels of physical activity after ACLR. However, most individuals experience persistent changes to lower extremity biomechanics well after completing structured rehabilitation and being cleared to return to activity. Despite this, there is little data available on individuals with an ACLD, or ACL-reconstructed ACLR knee and biomechanical alterations leading to the development of OA. Numerous studies that have investigated walking gait have found significant reductions in peak internal knee extensor moment, and small reductions in peak knee flexion angle, with individuals adopting a quadriceps avoidance gait pattern during walking. One of the most common activities pre- and post- surgery is running, and it is not known whether individuals before and after ACLR knee have different knee kinematic and kinetic patterns to healthy individuals. However, in general clinical practice, the option to ask the individual to run and to assess this is limited, and so a more space-optimised clinical assessment is needed. Therefore, the single leg squat (SLS) has been chosen as the measure to assess these individuals. No previous study has been found on kinematics and kinetics before and after ACLR during running and SLS. Therefore, the research question of this thesis is to determine whether there is an alteration in the kinematics and kinetics of hip and knee joints, along with the related risk factors for patellofemoral pain syndrome and OA, before and after ACLR during running and SLS.

This research aimed, in the first study, to establish within-day and between-days reliability for the use of 3D motion analysis to measure the biomechanical variables for running and SLS tasks. This study concludes that for between and within-day sessions, specific variables demonstrated good and excellent levels of consistency (ICC=0.80-0.99), and exhibited standard errors of measurement that have relatively low values.
The second study investigated the hip and knee joints’ kinematics and kinetics six to eight months after ACLR, and compared the outcomes between the injured limb and non- injured limb (n=34), and a control group (n=34). This showed that ACLR individuals, despite a return to sport and being deemed medically fit, still have performance issues, which could be related to PF joint pathology and OA. This study found that the injured limb of the ACLR group showed a significant reduction in peak internal knee extensor moment and impulse, knee flexion angle and external knee adduction moment (p=0.01, p=0.01, p=0.01, p=0.04 respectively) compared to the control group during running. On comparing the injured and non-injured limbs in ACLR, an increase in hip internal rotation angle, coupled with a reduction in knee flexion angle, peak internal knee extensor moment and impulse (p=0.01, p=0.01, p=0.01, p=0.01 respectively) was found during running. Comparing the injured and non- injured limbs in SLS, revealed an increase in hip internal rotation angle coupled with knee adduction angle, in addition to a reduction in peak internal knee extensor moment (p=0.01, p=0.01, p=0.04 respectively). The control group compared to the injured limb of the ACLR group during SLS, showed reductions in peak internal knee extensor moment (p=0.01); whereas the non-injured limb of the ACLR group revealed an increase in hip internal rotation moment, and a reduction in peak internal knee extensor moment (p=0.04, p=0.01 respectively).

The third study investigated hip and knee joint kinematics and kinetics before, and three and six months after ACLR, during running and a SLS task to compare between the injured limb and non-injured limb (n=6), and the control group (n=6). This was to examine whether these factors develop over time, which could be related to PF joint pathology and OA. The findings show that there was a reduction in the peak internal knee extensor moment and impulse three and six months post ACLR between limbs, and in comparison to the injured limb for the ACLR group and the control group (p=0.01, p=0.01 respectively). In addition, significant differences were noted before, and three and six months after ACLR, during running (p=0.01, p=0.01 respectively), as well as SLS between limbs three months after ACLR. At the same time, within the ACLR group, there was a significant reduction in knee flexion angles during running three and six months after ACLR between limbs.

The results of this thesis show that following ACL reconstruction, individuals in this thesis showed some specifically altered knee joint kinematics and kinetics. The reduction in peak internal knee extensor moment and knee flexion angle was in an effort to reduce or avoid the contraction of the quadriceps; namely, quadriceps avoidance. These reductions may
contribute towards patellofemoral joint disorders, thereby increasing the risk of degenerate joint disease commonly found post-surgery. The results of this thesis may help to guide the development of new or alternative treatment options for improving long-term joint health after an ACL injury.